1. Field of the Invention
The present invention relates to the technical filed of cryptographic key generation and, more particularly, to a biometrics-based cryptographic key generation system and method.
2. Description of Related Art
Cryptographic keys are widely used in access control to computing resources, bank accounts in ATM systems, and user validation in e-business. Conventionally, system random-selected or user-determined PINs and passwords are utilized to generate unique keys for access control. However, system random-selected keys are easy to forget and user-determined keys are subject to dictionary attacks and also easy to transfer thereby resulting in security concerns. Relatively, biometrics, such as face, voice, iris and fingerprint, contribute specific characteristics of each individual. Therefore, biometric data potentially can be taken as good alternatives or supplements to PINs and passwords to provide a higher safety control.
Biometrics-based authentication can be mainly classified as two mechanisms: (1) biometrics-based authentication access control mechanism; and (2) biometrics-based cryptographic key generation mechanism. Please refer to FIG. 1. FIG. 1 illustrates the system structure of the biometrics-based authentication access control mechanism which achieves access control according to the biometrics-based authentication method. In the system registration phase, the access control mechanism transforms user's biometric features into a template; in the authentication phase, the mechanism utilizes the template to perform a comparison with user's biometric features. If user's biometric features match the template, the user is confirmed as an authentic user and able to access personal information protected under the system. The personal information includes cryptographic keys, smart cards, or information for other access control purposes, such as wireless communication, or system resources. Further, the access control mechanism can directly transform the adopted template into the cryptographic key once user's biometric features match the template.
However, though the aforesaid access control mechanism can adjust the tolerance for biometric feature diversities by adjusting parameters of the comparison mechanism, the template still may reveal complete information regarding user's biometric features. Consequently, the comparison between the template and user's biometric features should be performed under an absolutely secure environment. Otherwise, user's personal information would be seriously threatened.
With reference to FIG. 2, there is shown a system structure of the biometrics-based cryptographic key generation mechanism. This mechanism is different from the aforementioned access control mechanism in the way of generating the template. In this mechanism, the template is obtained by performing an operation to registered biometric features and a password generated by a random number generator 21. Therefore, in the authentication phase, the password can be obtained after performing an inverse operation to the inputted biometric features and the template. The operations could be addition, subtraction, multiplication, division, and XOR operation.
In the above system structure, the password can only be accurately generated by performing the inverse operation to the correctly inputted biometric features with the template stored in the system. Therefore, even successfully capturing the template, an impostor or attacker still cannot access user's cryptographic key such that the safety of usage is significantly improved. However, since this kind of mechanism doesn't have any comparison mechanism for adjusting the tolerance to the diversity of biometric features, very stable biometric features, such as fingerprints, have to be adopted under strict criteria (e.g. using a specific device, or applying a specific algorithm) in order to generate stable biometric features during each usage.
To eliminate this drawback, U.S. Patent Publication No. 2003/0219121 proposes a solution by adding an error correction code to the password, so as to tolerate the incorrectly inputted password within a fixed number of error bits and automatically correct the password. However, because biometric features may vary with individual dimensional diversities, adding the error correction code still fails in optimizing the tolerance adjustment for individual dimensional diversities.
A known cryptographic key generation method is proposed to perform binarization to biometric features in each dimension (F. Monrose, M. K. Reiter, Q. Li, and S. Wetzel, “Cryptographic key generation from voice,” Proceedings of the 2001 IEEE Symposium on Security and Privacy, pp. 202˜213, May 2001). Therefore, a fixed password can be generated by utilizing a secret sharing scheme (A. Shamir, “How to share a secret,” Communications of the ACM, Vol. 22, No. 11, pp. 612-613, November 1979) even if biometric features have diversities under certain dimensions. However, this solution is only suitable for binarized biometric features. Furthermore, since diversities are only divided into stable diversities and unstable diversities, the characteristic that biometric features in different dimensions have different distinguishabilities and different degrees of diversities are still not thoroughly considered and utilized.
Based on the above analysis, a satisfactory biometrics-based cryptographic key generation mechanism should be capable of not only preventing the adopted information, such as templates, from revealing user's authentic biometric feature information, but also tolerating the characteristic that inputted biometric features have different diversities in different dimensions. Moreover, besides the diversity issue, the key space of the generated cryptographic key could be much more expanded if taking different degrees of distinguishabilities with biometric features in different dimensions into consideration.
Therefore, it is desirable to provide an improved biometrics-based cryptographic key generation system and method to mitigate and/or obviate the aforementioned problems.